Great, I wasn't aware this was possible. Could you point me to the documentation on how to do this?

What I would like to do is for a user who has say 2 computers and 1 license, to easily switch between using the software on either computer, but to not be able to run it on both computers at the same time.

I would warn that this belongs to only Enigma Protector - Online Solutions, the version that supports online activation. Standard version does not have this ability.

Ok, if you have a project configured with online activation, to deactivate a license from application you just need to call a function EP_ActivationDeactivate. If the function succeded then server part accepted deactivation and user can move the license to another computer. The system won't allow the customer to install a license on another computer without deactivation of previous.

Number of allowed activated computers can be also managed from a web part.

Once the license becomes deactivated, you can check it by selecting necessary customer in the Customers page at web part. There will be a list of the licenses ever activated by customers and active licenses will be ticked with checkbox. You can manually deactivate a license from a web part, but this is not recommended.

This information is actual for the new version of Enigma Protector 6.00